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Title: Indigestion : a study of some of the nervous mechanisms concerned in the production of functional disorders of the stomach
Author: Lucraft, Harry S.
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1924
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Digestive derangement, in one form or another, is one of the commonest ailments that the general practitioner is called upon to treat. A very short experience of general practice is sufficient to demonstrate this; and the fact is soon apparent, also, that in only a small proportion of patients complaining of digestive troubles can actual organic disease be detected. In the vast majority of cases the trouble is of a minor nature, and not dependent on any actual organic change in the organs, but sufficient, nevertheless, to cause much real suffering and debility; and the problem of "indigestion" is a very real one. In many of these cases, examination of the stools may show no abnormality whatever. X-ray examination and test meals may reveal no striking departure in motility and secretion from the standard generally recognised as normal; and the "indigestion" in these cases does not stand for non-digestion, but for discomfort during the process of digestion. Furthermore, X-ray observations have shown that even in health there may be wide variations in the size and shape of the stomach, which the fractional test meal shows considerable variations in the composition of the gastric juice of apparently normal individuals. Similar* variations occur in "indigestion". The patient complaining of greatest distress may be the possessor of a hypertonic, a hypotonic or a "normal" stomach; while in the matter of secretion he may show excessive secretion, "normal" secretion, or none at all. Prom clinical examination alone, therefore it is difficult to say exactly what is going on in the stomach, and what are the actual conditions of tone, etc., in the gastric wall. Sir James Mackenzie says "Attempts are continually being made to classify affections of the stomach, and the lack of agreement in these classifications is merely due to the fact that attempts are made to differentiate what cannot be differentiated . . . To ascertain the true nature of many stomach affections it is necessary to wait and observe the results of treatment and the progress of the disease". This is at present, unfortunately, only too true. We must remember, also, that functional disorder of one part of the alimentary canal/frequently depends on organic disease of some other part. Consequently, however convenient it may be for descriptive purposes to classify as complete diseases disorders of limited sections of the alimentary tract, we must always, in dealing with actual cases of disease, consider the tract as a whole. As Mackenzie points out, there is a great similarity in the symptoms of gastric diseases of the most varied kinds; most gastric symptoms are of a reflex nature, and capable of being produced by stimuli arising from the most varied causes, trivial or severe. Nevertheless it is reasonable to hope that increased knowledge of these reflexes and of the stimuli capable of calling them into action may yet enable us to differentiate many of the minor or functional derangements of the stomach, and so give us the clue to the correct method of treatment. The importance of reflex phenomena in the case of the salivary glands was pointed out many years ago by Pavlov, who showed the variations that occur in the amount and the character of the salivary secretion with variations in the kind of stimuli presented to the buccal mucous membrane. Dry foods, for instance, such as meat powder or biscuit powder when introduced into the mouth of a dog with a salivary fistula, produced a much stronger flow of saliva than moist foods. Sprinkling an indifferent dry powder on the tongue excited one gland to activity and not another. Different chemical stimuli such as salts, bitters, acids, alkalies, gave characteristic responses from the different glands as regards the quality of saliva, the seat of action and the influence of local conditions on the results. These results depend on the discriminating ability of the peripheral end organs of the afferent nerves of the buccal mucous membrane in determining the nature of the material present in the mouth, and the amount and composition of the saliva best calculated to deal satisfactorily with it. Section of the nerves destroys the nicely calculated nature of the glandular response, and we must conclude with Pavlov that the sensory nerve endings in the buccal mucous membrane "officiate in deciding the most minute, exact, and highly specialised adaptation of the salivary glands to the nature of objects on which their secretions are poured out". Pavlov showed, furthermore, that in dogs previously experimented on in this way, a response could be obtained from the glands by means of "psychic excitation". Thus in a dog with a salivary fistula, a flow of saliva is at once obtained on merely showing the animal a piece of meat. The saliva is of a viscid, stringy nature, corresponding to that secreted when the animal is actually eating meat. If now the meat he removed, and pretence is made of introducing quartz pebbles into the mouth, no flow of saliva occurs (such pebbles do not stimulate the secretion of saliva, when actually introduced into the mouth). If, however, the pebbles are replaced by sand, and the dog (who has had previous experience of the introduction of fine sand into the mouth) imagines that the sand is to be again put in the mouth, a free secretion of thinner less stringy saliva is at once produced. Similarly, also, the sight of a bottle containing dilute acid (if associated in the mind of the animal with previous experiments), and the pretence of introducing such acid into the mouth, at once produces a free flow of saliva. This psychic excitation of course, can only occur in "educated" animals, and the reflexes involved have their starting point not in the end organs of the afferent nerves of the buccal mucous membrane, but in the end organs of eyes, nose and ears. Many factors enter into the production of the phenomenon, which depends, in part at least, for its successful accomplishment, on such incidental conditions as the surroundings of the animal, the presence of familiar attendants, the vessel containing the food or other material, etc. The results of the experiment therefore, are not so uniformly and unconditionally certain as in the case of direct stimulation of the buccal mucous membrane. The effect, in the case of the psychic stimulation, is dependent on a far greater number of conditions than in the physiologic, and the psychic reflex is therefore a conditional one, but "it never occurs without perceptible stimulation of some sense organ from without". These examples illustrate the importance of reflex processes as affecting the salivary glands. Similar, though perhaps less easily demonstrable reflex processes, play as important a part in the regulation of the activity of the gastric glands; and it is hoped that increased knowledge of such gastric reflexes will result in a clearer conception of the significance of some obscure gastric symptoms. In the study of the symptoms produced by disease of the stomach, or of any other organ, a consideration of the nervous control and the regulating processes is of fundamental importance, as it is by derangement of these processes that many symptoms are produced. The stomach, in common with other parts concerned in the digestion and assimilation of food, is under the control of the involuntary nervous system. Stimuli originating in the stomach may produce reflex symptoms in distant organs, the impulses travelling over the nerve tracts of this system; and conversely stimuli arising at a distance may, in like manner, produce end results in the 3tomach. Before passing to a study of disordered gastric function, therefore, it is necessary to examine not only the nerve supply of the stomach, but the connections and distribution of the involuntary nervous system as a whole.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (M.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available